Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Installation and Use of Meteorological Tower Systems

Melanie A. WetzelDesert Research Institute

and

University of Nevada, Reno

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Objectives

Approach the use of instrumented tower systems as a process

Present technical options for sensor and tower characteristics

Describe factors and decisions critical to installation

Provide examples of tower system applications

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Why Use Towers ? Standardization (generally to 10 m height) with respect to vertical profiles

of wind, temperature and other boundary layer parameters

Ability to apply parameterizations for other heights such as the logarithmic wind speed (S) vs. height (H) equation, Sa = Sb (Ha/Hb)

p

Exponent p is typically in the range 0.14 for smooth terrain to 0.25 for rough terrain

Reduction in blockage and shadowing from obstructions

Increased availability of solar power; improved communications

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Examples of Existing Networks AWOS and ASOS

Oklahoma MesoNet

MesoWest

SNOTEL

Highway Networks (DOT, States)

Air Quality Networks

DOE / ARM

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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System Design Factors

Sensor characteristics Tower access Transport, construction and

maintenance Data communications options Power source System expandability

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Process-Oriented Approach to System Design1. Select sensors 2. Specify data acquisition 3. Design power system 4. Program the datalogger 5. Install equipment 6. Plan heights for equipment installation 7. Design tower setup and installation procedures 8. Orient instruments 9. Install and initialize software 10. Maintain data collection and data quality

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Steps for Specifying Instrumentation Determine scope of project and potential applications Identify needs for simultaneous auxiliary data Select types of instrumentation (parameters, resolution, range) Determine sampling rates and length of study Acquire specific instruments (cost, availability, etc) Conduct analysis of extreme conditions (heat, cold, icing, wind)

Example of time averagingmeasurements from a sensor with low resolution

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Criteria for Sensor Selection Sensor range, resolution, precision Ruggedness and suitability for local

environmental conditions Cost of acquisition, operation and maintenance Availability (lead time, access to replacement

parts) Manufacturer history Software ease of use and compatibility Technical support Calibration requirements Time response and sampling frequency Compatibility with other sensors

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Data Acquisition Guidelines Determine data channel types and

number Calculate memory requirements Select data storage, access, editing and

merging methods Define protocol for missing data Determine procedures for identifying

drift or calibration errors

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Options for System Power Calculate power needed

Instruments Datalogger Communications Heaters

Evaluate power sources Direct power

(capacity, reliability) Fueled generators Wind and solar energy Battery reserve (temperature

effects and minimum capacity )

Provide adequate monitoring of power supply and interruptions

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Example of System Power Chart

Communications power drain is larger than sensor operation or data storage functions.

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Programming for Data Acquisition

Set up the datalogger program prior to field deployment

Develop data capture protocol (dial-in, site visit, etc)

Design data archival and documentation procedures

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Installation of Equipment at Site Assess possible hazards -- lightning, vandalism, animals, accidents Select location most appropriate to project objectives and longevity Avoid locales which are unrepresentative (fog, valley inversions) Identify and map potential obstructions or conditions

dust wind temperature solar illumination precipitation

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Proper Heights for Equipment Installation

Wind velocity standard height vs. wind turbine height

Solar panel location for site power vs solar energy survey

Need for multiple or non-standard heights

Access to control panel and communications

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Considerations for Tower Setup

Sensor placement

Sensor orientation

Shadowing

Wind blockage

Spatial representativeness

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Tower Types Poles with guy lines  Tripod

Triangular Sectioned Pivoting

Use of structures

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Orienting Instruments

Wind Vane

Radiative Sensors azimuth angle elevation angle

Reducing shadowing of precipitation, wind and other parameters

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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On-site Software Installation Test communications to and from

tower

Download program to site datalogger

Select and set time/date

Record local site parameters latitude/longitude elevation location on map

Tower Systems January 2001 -- AMS Short Course on Instrumentation

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Quality Control and Data Management Prescribe schedule to routinely check

data quality Monitor power supply Assess need to relocate sensors Evaluate benefits of sensor upgrade Prepare documentation for

operations and training: Standard Operating Procedures Site photos and diagrams Log sheets for maintenance Data format and archival schedule Sensor calibration history 

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ReferencesDaley, R., 1991: Atmospheric Data Analysis. Cambridge University Press, 457 pp.

DeFelice, T.P., 1998: An Introduction to Meteorological Instrumentation and Measurement, Prentice Hall, New Jersey, 229 pp.

Webster, J.G., ed., 1999: The Measurement, Instrumentation and Sensors Handbook. CRC Press, 916 pp.